FUNCTIONS OF VIGILANCE BEHAVIOR IN MAMMALS - A REVIEW

The functional approach to vigilance behaviour in mammals aims at understanding how it is influenced by natural selection, in correlation with survival chances and/or reproductive success. The main functions attributed to this behaviour are: detection of predators, observation of group members, location of food and avoidance of kleptoparasitism. Principal results obtained in mammals are consistent in showing that individual vigilance decreases and collective vigilance increases with increasing group size, that peripheral individuals are more vigilant than central ones and that males scan more than females during rutting period. This latter difference disappears after parturition. However, inconsistent or contradictory results concerning the influence of age, social rank, habitat and proximity of refuge do not allow determination of obvious relationships. Concurrently to those field studies, modelling the vigilance behaviour consists in estimating individual survival probability which would depend directly on the tradeoff between foraging and vigilance behaviour. However, inaccurate assumptions in the published models do not allow to consider the interspecific and intraspecific variability nor to make precise quantitative predictions. These models also raise the problem of the choice of a time scale to calculate an optimum in decision making.